A 66-year-old diabetic man presented to the emergency department with 3 days of abdominal distension and constipation. There was no history of neurologic and urologic disorders. A giant bladder was detected with abdominal ultrasound and computed tomography (CT). A total of 10,500 mL of urine was drained with urinary catheter. The diagnosis was neurogenic bladder due to diabetes mellitus with autonomic neuropathy. This is the largest volume of bladder in the literature.